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Rogister Y.,University of Strasbourg | Memin A.,University of Tasmania | Memin A.,University of Nice Sophia Antipolis | Rosat S.,University of Strasbourg | And 3 more authors.
Geophysical Journal International | Year: 2016

The geocentre motion is the motion of the centre of mass of the entire Earth, considered an isolated system, in a terrestrial system of reference. We first derive a formula relating the harmonic degree-1 Lagrangian variation of the gravity at a station to both the harmonic degree-1 vertical displacement of the station and the displacement of the whole Earth's centre of mass. The relationship is independent of the nature of the Earth deformation and is valid for any source of deformation.We impose no constraint on the system of reference, except that its origin must initially coincide with the centre of mass of the spherically symmetric Earthmodel. Next, we consider the geocentre motion caused by surface loading. In a system of reference whose origin is the centre of mass of the solid Earth, we obtain a specific relationship between the gravity variation at the surface, the geocentre displacement and the load Love number h'1 1, which demands the Earth's structure and rheological behaviour be known. For various networks of real or fictitious stations, we invert synthetic signals of surface gravity variations caused by atmospheric loading to retrieve the degree-1 variation of gravity. We then select six well-distributed stations of the Global Geodynamics Project, which is a world network of superconducting gravimeters, to invert actual gravity data for the degree-1 variations and determine the geocentre displacement between the end of 2004 and the beginning of 2012, assuming it to be due to surface loading. We find annual and semi-annual displacements with amplitude 0.5-2.3 mm. © The Authors 2016.

Scaini C.,Barcelona Supercomputing Center | Felpeto A.,Instituto Geografico Nacional IGN | Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Carniel R.,University of Udine | Carniel R.,National Research University of Information Technologies
Journal of Volcanology and Geothermal Research | Year: 2014

This paper presents a GIS-based methodology to estimate damages produced by volcanic eruptions. The methodology is constituted by four parts: definition and simulation of eruptive scenarios, exposure analysis, vulnerability assessment and estimation of expected damages. Multi-hazard eruptive scenarios are defined for the Teide-Pico Viejo active volcanic complex, and simulated through the VORIS tool. The exposure analysis identifies the elements exposed to the hazard at stake and focuses on the relevant assets for the study area. The vulnerability analysis is based on previous studies on the built environment and complemented with the analysis of transportation and urban infrastructures. Damage assessment is performed associating a qualitative damage rating to each combination of hazard and vulnerability. This operation consists in a GIS-based overlap, performed for each hazardous phenomenon considered and for each element. The methodology is then automated into a GIS-based tool using an ArcGIS® program. Given the eruptive scenarios and the characteristics of the exposed elements, the tool produces expected damage maps. The tool is applied to the Icod Valley (North of Tenerife Island) which is likely to be affected by volcanic phenomena in case of eruption from both the Teide-Pico Viejo volcanic complex and North-West basaltic rift. Results are thematic maps of vulnerability and damage that can be displayed at different levels of detail, depending on the user preferences. The aim of the tool is to facilitate territorial planning and risk management in active volcanic areas. © 2014 Elsevier B.V.

Calvo M.,University of Strasbourg | Calvo M.,Instituto Geografico Nacional IGN | Rosat S.,University of Strasbourg | Hinderer J.,University of Strasbourg | And 3 more authors.
International Association of Geodesy Symposia | Year: 2014

The Gravimetric Observatory J9 located near Strasbourg (France), has a long history of recording solid Earth tides. We present here one of the longest available gravity records (1973–2011) from three different instruments operating at the J9 station: a LaCoste– Romberg spring gravimeter (ET005) from 1973 to 1985, a GWR (TT70–T005) superconducting gravimeter from 1987 to 1996 and a GWR compact superconducting gravimeter (C026) since 1996. We give the results of a tidal analysis performed with ETERNA on these data sets. We show the improvement in terms of noise levels from the oldest type to the newest one and check the time stability of the observed tides for every instrument. This stability is also dependent on the stability of the scale factor of the cryogenic gravimeter which is derived from a direct comparison with repeated absolute gravity measurements. The response of the three gravimeters to the atmospheric pressure changes is also checked. With all these results we found that the improvement from a mechanical spring gravimeter to a modern cryogenic instrument is obvious. And also that the improvement from the T005 SG to the C026 SG is less impressive than from L&R to the T005 SG, but still notable. © Springer-Verlag Berlin Heidelberg 2014.

Tarraga M.,CSIC - Institute of Earth Sciences Jaume Almera | Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Abella R.,Instituto Geografico Nacional IGN | Carniel R.,University of Udine | And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2014

Geophysical and geochemical signals recorded during episodes of unrest preceding volcanic eruptions provide information on movements of magma inside the lithosphere and on how magma prepares to reach the surface. When the eruption ensues continuous volcanic monitoring can reveal the nature of changes occurring in the volcano's plumbing system, which may be correlated with changes in both eruption behaviour and products. During the 2011-2012 submarine eruption of El Hierro (Canary Islands), the seismic signal, surface deformation, a broad stain on the sea surface of the eruption site, and the occasional appearance of floating lava balloons and pyroclastic fragments were the main observable signs. A strong continuous tremor in the vent accompanied the eruption and varied significantly in amplitude, frequency and dynamical parameters. We analysed these variations and correlated them with changes in the distribution of earthquakes and in the petrology of the erupting magma. This enabled us to relate variations in tremors to changes in the (i) stress conditions of the plumbing system, (ii) dimensions of the conduit and vent, (iii) intensity of the explosive episodes, and (iv) rheological changes in the erupting magma. The results obtained show how the tremor signal was strongly influenced by stress changes in the host rock and in the rheological variations in the erupting magma. We conclude that the tracking of real-time syn-eruptive tremor signals via the observation of variations in plumbing systems and magma physics is a potentially effective tool for interpreting eruption dynamics, and suggest that similar variations observed in pre-eruptive tremors will have a similar origin. © 2014 Elsevier B.V.

Marti J.,CSIC - Institute of Earth Sciences Jaume Almera | Sobradelo R.,CSIC - Institute of Earth Sciences Jaume Almera | Felpeto A.,Instituto Geografico Nacional IGN | Garcia O.,Instituto Geografico Nacional IGN
Bulletin of Volcanology | Year: 2012

Recent studies on Teide-Pico Viejo (TPV) complex have revealed that explosive activity of phonolitic and basaltic magmas, including plinian and subplinian eruptions, and the generation of a wide range of pyroclastic density currents (PDCs) have also been significant. We perform a statistical analysis of the time series of past eruptions and the spatial extent of their erupted products, including lava flows, fallout and PDCs. We use an extreme value theory statistical method to calculate eruption recurrence. The analysis of past activity and extent of some well-identified deposits is used to calculate the eruption recurrence probabilities of various sizes and for different time periods. With this information, we compute several significant scenarios using the GIS-based VORIS 2 software (Felpeto et al., J Volcanol Geotherm Res 166:106-116, 2007) in order to evaluate the potential extent of the main eruption hazards that could be expected from TPV. The simulated hazard scenarios show that the southern flank of Tenerife is protected by Las Cañadas caldera wall against lava flows and pyroclastic density currents, but not against ash fallout. The Icod Valley, and to a minor extent also the La Orotava valley, is directly exposed to most of TPV hazards, in particular to the gravity driven flows. This study represents a step forward in the evaluation of volcanic hazard at TPV with regard to previous studies, and the results obtained should be useful for intermediate and long-term land-use and emergency planning. © 2011 Springer-Verlag.

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